(1) Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor integrated circuit component that is used for a communication device, a radio equipment and the like.
(2) Description of the Related Art
In recent years, a high frequency signal is mostly used for the communication device and the radio equipment, and a field effect transistor (hereafter referred to as FET) using gallium arsenide (hereafter referred to as GaAs) which has a good high frequency characteristic is used for a switch circuit of the semiconductor integrated circuit component included in the communication device and the radio equipment.
FIG. 1A is a functional block diagram showing an internal structure of the conventional semiconductor integrated circuit component (refer to Japanese Laid-Open Patent Publication application No. 11-144012).
The semiconductor integrated circuit component is composed of a control unit 600, a signal processing unit 601 and terminals 602. The control unit 600 controls the signal processing unit 601 based on a control signal inputted from the outside. The signal processing unit 601 is connected to the control unit 600 and performs a switching operation of a high frequency signal. The terminals 602 are interfaces between the control unit 600 and the signal processing unit 601, and the outside.
FIG. 1B is an external drawing of the semiconductor integrated circuit component.
The conventional semiconductor integrated circuit component includes a control semiconductor chip 610, a switch circuit semiconductor chip 611, a substrate 612, external terminals 613, and gold wires 614. The control semiconductor chip 610 is the control unit 600 using silicon (hereafter referred to as Si) as a base material. The switch circuit semiconductor chip 611 is the signal processing unit 601 using GaAs as a base material. The control semiconductor chip 610 and the switch circuit semiconductor chip 611 are mounted next to each other on the substrate 612, and the external terminals 613 are the terminals 602. The gold wires 614 connect, without crossing and touching other wires, i) between the external terminals a to h and the switch circuit semiconductor chip 611, ii) between the external terminals i to k and the control semiconductor chip 610, and iii) between the control semiconductor chip 610 and the switch circuit semiconductor chip 611 Here, Metal-Insulator-Metal type capacitors (hereafter referred to as MIM capacitor) 630 are formed on the switch circuit semiconductor chip 611, and the MIM capacitors 630 are connected to the external terminals e to h by the gold wires 614.
FIG. 1C is a diagram showing an example of a circuit structure of the semiconductor integrated circuit component.
The circuit of the semiconductor integrated circuit component includes a logic circuit formed on the control semiconductor chip 610 and a switch circuit formed on the switch circuit semiconductor chip 611.
In the logic circuit composed of Complementary Metal-Oxide-Semiconductor contact type elements (CMOS), input terminals are connected to external terminals 613 and output terminals are connected to each gate of switch elements 631 and shunt elements 632 via resistance elements 633. Further, the logic circuit generates ON/OFF voltage applicable to control the switch elements 631 and shunt elements 632 according to an external direct current (DC) signal and apply the ON/OFF voltage to the switch elements 631 and the shunt elements 632, where the external direct current signal is a control signal inputted from the outside. Here, the external direct current signal is an electronic signal binarized into high and low voltages having about one microminute or more of rise and fall times.
The switch circuit is composed of four MIM capacitors 630 connected to earth terminals e to h, four switch elements 631 connected between terminals a to d, four shunt elements 632 whose source or drain is connected to the MIM capacitors 630, and resistance elements 633.
Here, the switch elements 631 are FET so that they become either in a high impedance state or in a low impedance state depending on the ON/OFF voltage applied by the logic circuit, and pass or cut a high frequency signal from several MHz to several tens of GHz that transmits between terminals a to d.
Furthermore, since the shunt elements 632 are FET, they become either in the high impedance state or in the low impedance state depending on the ON/OFF voltage applied by the logic circuit, and the earth terminals a to d via the MIM capacitors 630.
Next, an example of operations of the semiconductor integrated circuit component having the structure as mentioned above is explained.
As shown in FIG. 1C, when connecting between the terminal a and the terminal b, it is assumed that, among the switch elements 631 and the shunt elements 632, the switch element 631 A and the shunt elements 632 G and H are in the low impedance state that indicates a state of ON, and the switch elements 631 B, C and D and the shunt elements 632 E and F are in the high impedance state that indicates a state of OFF. At this time, the transmission of the high frequency signal between terminals is cut except between the terminal a and the terminal b only where the high frequency signal is transmitted. Here, a logic operation is previously built in the control semiconductor chip 610, and the switch circuit semiconductor chip 611 has logic states, for the logic operation, at least as many as the number of combinations among terminals to be transmitted.
Thus, the conventional semiconductor integrated circuit component realizes, by using GaAs which has a better insulation capability than Si as a base material of the switch circuit semiconductor chip, a reduction in a loss of the high frequency signal of the switch elements and the shunt elements in the state of ON, that is, a reduction of an insertion loss of the switch circuit. In addition, the conventional semiconductor integrated circuit component realizes a reduction in leakage of the high frequency signal of the switch elements and the shunt elements in the state of OFF, that is, to improve the isolation characteristic of the switch circuit. Furthermore, the conventional semiconductor integrated circuit component realizes a cost reduction by using Si whose cost is lower than that of GaAs, as the base material for the control semiconductor chip 610 which does not have transmission paths for the high frequency signal.
As mentioned above, in the conventional semiconductor integrated circuit component, GaAs, which is a rare natural material as compared with Si, is used as the base material for the switch circuit semiconductor chip. However, pluralities of switch elements, shunt elements and MIM capacitors are formed on the switch circuit semiconductor chip so that the area of the switch circuit semiconductor chip is enlarged, which causes an increase of the cost of producing the semiconductor integrated circuit component.
Also, in the conventional semiconductor integrated circuit component, the high frequency signal is transmitted via gold wires that connect the MIM capacitors to the external terminals. However, as shown in FIG. 1B, the length of the gold wires connecting the MIM capacitors to the external terminals e to h are long. Therefore, parasitic inductance by the gold wires is largely affected so as to increase the insertion loss of the switch circuit, and the isolation characteristic is deteriorated.
Further, in the conventional semiconductor integrated circuit component, in the case where an integration density of the switch circuit semiconductor chip is increased by further forming elements that are necessary for the operation of the switch circuit on the switch circuit semiconductor chip, the area of the switch circuit semiconductor chip is increased and the area of the substrate on which the switch circuit semiconductor chip is mounted is increased as well, thereby extending the size of the semiconductor integrated circuit component. In other words, the number of elements to be mounted on the switch circuit semiconductor chip is restricted by the area of the substrate on which the semiconductor chip is mounted so that the integration density of the semiconductor integrated circuit component cannot be increased without extending the size of the semiconductor integrated circuit component.
Lastly, in the conventional semiconductor integrated circuit component, the reduction of the insertion loss and the improvement of the isolation characteristic of the switch circuit are realized by using GaAs as the basic material for the switch circuit semiconductor chip. However, the insertion loss and the isolation arise from a solid-state value of the semiconductor such as an electrical conductivity and a dielectric constant, and the solid-state value has a breaking point. Therefore, the solid-state value determines the limits of the insertion loss and the isolation so that the insertion loss of the switch circuit cannot be reduced further and the isolation characteristic cannot be improved further. For example, as for the electrical conductivity, the value of the electrical conductivity of the semiconductor is 1×103 S/cm, which is three figures lower than the value of the electrical conductivity of the metal 1×106 S/cm. As for the dielectric constant, the value of the dielectric constant of the semiconductor is 12, which is a single figure higher than the value 1 of the relative dielectric constant of the air. As a result, a small insertion loss as in metal and a high isolation as in air cannot be realized in the semiconductor.
Here, a method of controlling a channel width is suggested as a method of realizing a further reduction of the insertion loss of the switch circuit and an improvement of the isolation characteristic of the switch circuit since the loss and leakage of the high frequency signal are determined by a resistance value when FET is in the state ON. However, this method cannot realize the reduction of insertion loss and the improvement of the isolation characteristic at the same time because the insertion loss and the isolation are in a tradeoff relationship. In other words, setting the channel width of FET larger lowers a resistance value in the state of ON and reduces the loss of the high frequency signal so as to increase the leakage of the high frequency signal. Also, setting the channel width of FET smaller lowers the capacitance value in the state of OFF and reduces the leakage of the high frequency so as to increase the loss of the high frequency signal.
Furthermore, a method of using only MEMS (Micro Electro Mechanical Systems) switches for manufacturing the semiconductor integrated circuit component is suggested as a method of further reducing the insertion loss of the switch circuit and improving the isolation characteristic, where the MEMS switch is a switch device using MEMS technology. For example, the MEMS switch has a small insertion loss of 0.1 dB and an isolation of 40 dB as high as that of the air which cannot be achieved by the semiconductor. However, the MEMS switch needs a micro space structure at a mechanical contact point so that a complicated manufacturing process for a space formation is required. Additionally, since conditions for the space formation to manufacture the MEMS switch need to be the same as possible, designing a space between elements and an arrangement of elements equally as possible for each element is restricted. Therefore, it is difficult to manufacture the semiconductor integrated circuit component only by using the MEMS switches. This method also cannot realize a reduction in the insertion loss and improve the isolation characteristic.